Small engine accessory devices not directly driven by an engine, and especially such intermittently operated devices as automatically controlled valves and switches for vehicle air conditioning or emission control systems, are generally actuated by carburetor manifold vacuum. However, the use of engines without carburetors or with widely varying manifold vacuum levels suggests the use of some other source of power for actuation of these accessory devices. Engines equipped with an engine driven air pump providing secondary air flow for exhaust emission control purposes already have a source of air at positive pressure which is available for intermittent use.